We have our family staying with us at the moment, so have high demand for hot water. We’re having problems with hot taps taking time for hot water to come through and sometimes hot water running cold. A plumbing engineer thinks there may be a crossed pipe between hot and cold supply but it’s hard to know where. Before we start ripping into the structure of the house I wondered if anyone has experience of using ground penetrating radar or other non-destructive testing to try to pinpoint the problem.
I’m clutching at straws I know but want to try to exhaust all options before we bring in the jack hammers.
I can’t help with your specific query, but that seems an odd explanation for your problem, especially if the HW problems not experienced until abnormally high demand. Questions worth considering include: Are there are multiple outlet locations does the same happen everywhere or only one? If multiple, when the water goes cold at one, does it also run cold at another? Is it a tank or combi system? (Both can run out with high demand - see the current Boiler options thread.) How long is the pipe run from tank or combi to the outlet(s)? Your plumber may of course have considered in a lot of detail and done extensive checking, but in my experience many tradespeople are not that great at anything out of the very ordinary.
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The engineer did some thorough investigation, and concluded that cold water was entering the hot supply somewhere. We had noticed issues previously, but not as bad / regular.
We can get, say, hot water to a tap by running it for up to a minute and then it stays hot with the water running. Turn off the tap and it will run cold again after leaving it a few minutes.
Up to a minute doesn’t sound long at all to me if the pipes run some distance from the tank/combi - and I’ll bet the pipes are not insulated - Other than all I’ve done myself I’ve yet to come across any hot water or CH pipes insulated except when in a loft space.
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Sorry to drip feed information. Hadn’t realised we would get into diagnosis. Sometimes the only way to get hot water to an outlet is to open another outlet nearby. Also showers can suddenly run cold even though there’s no demand added and there’s plenty of hot water in the tank.
That makes me wonder if the shower connection at the tank fir the shower feed is too low down to access all the hot water. If it was due to a connection also to cold I’d expect the effect to be constant, or at least happening when someone is not drawing cold water from somewhere, possibly the cold flow stopping when someone is using a cold outlet.
The draw water from one outlet before being able to get any from another is puzzling me at present…
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I’d turn off the mains stop tap, and see if it has any effect on the DHW flow, plus see if any water comes out of the cold water taps.
Also, lower the mains flow by closing the mains stop tap a little, and see what happens.
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Ok for completeness we have a standard condensing boiler feeding a pressure system (no header tanks.) There are pressure control valves in both hot and cold feeds. With the hot water from the tank isolated there is cold water flow through mixer taps suggesting cold water is cross feeding into the hot supply pipe work.
Happy to add more detail if it helps.
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That is - in my view - very difficult to believe. Not convinced that this ‘Plumbing Engineer’ knows what is happening.
Much more likely to be something that happens only when you draw a lot of Hot Water.
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Now that is significant info. First question: is there a thermostatic valve anywhere in thd hot water system (between the tank and any outlets, not not counting any shower thermostatic control valves for now?
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I’m having a late sandwich, so i will be quick.
The first thing to do is just turn everything off in the house as in taps, etc, and see if the water meter is going round still, hopefully not. This then proves no leaks.
Then i would be looking at places where the hot and cold mix, being a combi system, then not many places normally, but shower valves, bath mixer, etc.
But on your bath, you may have a blending valve. This could be faulty and letting the water mix when it shouldn’t be.
Is the boiler operation ok, as in when you open a hot tap, it fires up and stays working.
Also, whilst we are at the boiler, check the heating flow doesn’t get warm when doing hot water, as this means the divertor valve in the boiler is letting by, this will result in poor hot water.
After that’s it starts getting to the point of needing to go look, as it could be something simple or not, but hard to say much more with the info i have.
Cheers dunc
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Just realised you haven’t got a combi boier miss read it.
So some off them things obviously dont apply.
I would be looking at shower valves and especially behind the bath panel, looking for that blending valve if you have one
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A possible test for cross flow. Turn off the Cold water at the Mains Tap.
Now turn on the hot water. Does this produce just good hot water?
Now while the hot water is running, turn on the cold water Mains to the house, then does the water flow increase, and does the water get colder
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Dunc and I are saying the sane thing (blending valve = thermostatic mixing valve), only I was thinking first look for one other than any thermostatic shower control ones. Thinking about it, if shower goes cold unexpectedly, with no other water draw, and with its HW tank draw point definitely in the still hot region, then maybe that shower valve itself is suspect (but less likely if two different showers exhibit same behaviour).
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The HW sounds like it is mains pressure, in which case tuning off the main stopcock would atop hot as well as cold.
fair point
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